The goal of this project is to utilize engineered forms of the enzyme cytochrome c peroxidase to demonstrate the feasibility of rational protein design towards the accomplishment of oxidative catalysis of specific organic reactions. The discovery that the active site Trp- 191 in the oxidized "ES" state of CCP is reversibly oxidized to a stable cation free radical has prompted an interest in exploiting the chemistry inherent at this site for the possible binding and/or oxidation of organic molecules. To this end, construction of the W191G mutant, in which the active site tryptophan was replaced with glycine, was recently reported, and the feasibility of small molecule binding to this site was clearly demonstrated. Part I of this proposal involves the systematic determination of the factors that control substrate specificity and binding within the cavity. Part II of this proposal involves an investigation of the oxidative chemistry of organic substrates, such as the aminothiazole anti-thyroid drugs, that are known to react with heme enzymes. Part III of this proposed study utilizes the information gleaned from Parts I and II of this proposal, and focuses on the feasibility of utilizing the W191G cavity mutant for the purposes of catalyzing general oxidation of organic substrates from within the cavity.